The present invention relates to data storage and retrieval systems, and more particularly to a head gimbal assembly having reduced airflow excitation.
Hard disc drives (HDDs) are well known in the art and comprise one or more discs, each disc having several concentric data tracks for storing data. When multiple discs are used, a stack is formed of co-axial discs having generally the same diameter. A transducing head carried by a slider is used to read from or write to a data track on a disc. The slider is carried by an actuator arm. As the disc is spun, the slider glides above the surface of the disc. The actuator arm, also known as a block arm or pivot housing arm, movably positions the slider with respect to the disc. A plurality of actuator arms may be connected to a common E-block for common rotation. The slider, suspended on the actuator arm, is positioned above a data track on the disc by moving the actuator arm about an axis using a large-scale actuation motor, such as a voice coil motor.
The slider is mounted on the actuator arm using a head gimbal assembly (HGA). A standard HGA comprises a baseplate, a load beam, a gimbal, a flexible interconnect circuit, and the slider. The load beam provides the main support structure for the HGA. The baseplate connects the load beam to the actuator arm, the baseplate also being swaged to the actuator arm. The baseplate is often connected to a bottom side of the load beam. In other embodiments, the baseplate is connected to an opposite (top) side of the load beam. In still further embodiments, a second baseplate is connected to the top of the load beam.
The gimbal is attached to the load beam opposite the baseplate. The gimbal and baseplate are each attached to the load beam by methods known in the art, such as spot welding. The slider is supported by the gimbal. The gimbal is designed to flex, allowing the slider to follow the surface of the disc more closely than if the slider were mounted directly on the load beam. The slider supports a transducing head, which may be a magnetoresistive (MR) element, for reading and/or writing to the data tracks on the disc.
The flexible interconnect circuit is located on one side of the load beam and provides the circuitry to and from the transducing head in the form of leads and traces. The leads and traces connect the flexible interconnect circuit to the slider and thus allow electronic signals to pass between the transducing head carried on the slider and the flexible interconnect circuit. The flexible interconnect circuit can have formations along its length, such as an elbow.
The number of discs utilized in a particular HDD system varies, and one or more discs may be used according to the desired storage configuration. As such, disc locations may be left empty to provide smaller storage capacities while minimizing manufacturing costs by utilizing a common housing and E-block structure. Further, the number of HGAs may be varied, allowing one or more HGAs to access each disc. Generally, one HGA is positioned relative to each side of every disc. Because an actuator arm can hold multiple HGAs, a single actuator arm disposed between two parallel, co-axial discs of generally the same diameter may have two HGAs attached, with the HGAs attached to opposite sides of the actuator arm. Thus, the single actuator arm is disposed between opposing faces of the two discs, allowing transducing heads on the two attached HGAs to access the opposed faces of the two discs.
Other actuator arms in the same HDD may have only a single HGA attached, such as when an actuator arm is disposed to access the outermost face of the outermost disc in a stack or to access an inner face of a disc in a stack where no other disc face is located nearby. Endcaps, which may also be referred to as swage plates or base plates, are used to balance actuator arms having a single HGA attached. Such endcaps provide balance to actuator arms in X, Y and Z directions about a centerline of the actuator arm, generally by matching thickness and weight characteristics of the endcap to thickness and weight characteristics of the HGA. Additionally, endcaps provide protection from distortion of the actuator arm during HDD fabrication. In particular, endcaps reduce a risk of distortion of the actuator arm while components are mechanically attached to the actuator arm.
Endcaps are connected to an end of the actuator arm where an HGA might otherwise be attached. Known endcaps generally have a swage hole centered on the endcap to mechanically swage the endcap to the actuator arm. Thus, an actuator arm in a single HGA configuration has the HGA and the endcap disposed on opposite sides of the end of the actuator arm. Endcaps may also be attached to either an upper or a lower side of an actuator arm devoid of HGAs.
As a spindle rotates the magnetic disc at a high speed, air movement adjacent a surface of the magnetic disc is accelerated to create a disc “wind.” The wind generally co-rotates with the disc. The co-rotating wind approaches an upstream portion of the actuator arm assembly defined as a windward side of the actuator arm assembly.
While a boundary layer of air generally co-rotates with the motion of the disc surface in a substantially symmetric manner, asymmetrical air flows can develop at or near the outer diameter of the rotating disc. Devices such as environmental control modules (ECMs), shrouds, fins and/or air dams may be used to control airflow both over the surface of the disc and beyond the outer diameter edge of the disc. However, manufacturing tolerances leave a significant gap between the outer edge of the rotating disc and the ECM, shrouds, fins and/or air dams. Current HDD designs generate significant turbulence at the outer diameter of the rotating disc.
When the HGA is positioned at or near the outer diameter of the disc, airflow can become turbulent at and around the HGA. Airflow can be especially turbulent where a portion of the HGA overhangs the outer diameter edge of the disc. At or near the outer diameter of the disc, air turbulence in the form of eddies, shedding, and other phenomena may cause excitation and vibration of the HGA. Excitation and vibration of the HGA can result in off-track movement of the transducing head. Specifically, discrete portions of the HGA can resonate, with those vibrations causing off-track movement by the entire HGA.
Windage excitation of the HGA when the HGA is at or near the outer diameter of the disc is most problematic when a single HGA is attached to the actuator arm. This may be because dual HGA configurations, meaning actuator arms having two HGAs attached on either side of the actuator arm, exhibit less windage excitation problems. Dual HGA configurations provide inherent shielding from air turbulence as the HGAs shields each other. Thus, “dummy” HGA attachments could be used to provide both balance and shielding, where on an actuator arm one HGA functions to access data and the other is a “dummy” assembly providing only balancing and shielding functionality. However, such a configuration is undesirable because the high cost of HGAs makes the use of a “dummy” HGA expensive and impractical.
Vibration of the HGA may be measured as non-repeatable runout (NRRO), which measures non-repeatable vibration due to random factors. As the recording density of magnetic discs continues to increase, the width or pitch of the tracks on the disc must decrease. This makes it increasingly difficult to hold the HGA above the selected data track. As track width or pitch becomes small, measured NRRO becomes large relative to the track pitch. Thus, the performance of the disc drive is more sensitive to errors caused by NRRO.
Thus, there is a need in the art for a disc drive design to control the amount of airflow excitation at the HGA to reduce NRRO.